The first coatings, according to the state of the art, which allowed an improved wear prevention against free surface wear to be obtained, were comprised of titanium carbide with a thickness up to 8 .mu.m. Further, double or multiple coatings of titanium carbide and titanium nitride, especially with titanium nitride as an outermost layer, are known in the art for reduced cratering when the product is used as a cutting insert in machining. For further improvement of such cutting inserts, multilayer coatings of the layer sequence TiC, Ti(C,N), TiN, have been proposed. It has been found that the natural brittleness of ceramics, like Al.sub.2 O.sub.3 can be minimized when Al.sub.2 O.sub.3 is applied in a thin layer form and thus, TiCTi(C,N) and an outer layer of Al.sub.2 O.sub.3 have been provided as multiple coatings. While the patent literature, for example EP 0 299 282 B1 describes in special cases the use of carbides, nitrides and/or carbonitrides of the elements titanium, zirconium, hafnium, vanadium, niobium and/or tantalum, these have been described only as useful in an example with titanium compounds as coating materials, in part in combination with aluminum oxide. The same is true with the description of ZrO.sub.2 in the combination with or as a replacement for oxide coatings. DE 36 20 901 A1 or EP 0 250 865 A1 which has the same content, describes for the first time a cutting tool whose cutting edge is coated with titanium carbide, titanium carbonitride and/or titanium nitride and whose outermost cover layer is composed of a thin zirconium nitride layer. The zirconium nitride, which has poorer wear characteristics than the aforementioned titanium compounds should hinder the oxidation of the base layer underlying this coating by atmospheric oxygen, whereby the good wear characteristics of the titanium carbide, titanium carbonitride and/or titanium nitride coatings can be fully maintained.
By contrast, in U.S. Pat. No. 3,854,991 (or CH A 585273) a coating of a sintered hard metal product is described in which the coating is comprised of HfCN and/or ZrCN and has an X-ray diffraction lattice constant which in the case of HfCN and a mixture of HfCN and ZrCN lies between 4.5570 and 4.630 angstrom and in the case of ZrCN lies between 4.6 and 4.62 angstrom. In the case of ZrCN the CN ratio is clearly less than 1. For the production of these hafnium or zirconium carbonitrides, a hafnium halogenide and/or a zirconium halogenide can be fed over a substrate together with hydrogen, nitrogen and a hydrocarbon at a temperature of 1000 to 1300.degree. C.
U.S. Pat. No. 4,714,660 describes a cutting insert of a CVD-coated substrate body in which the first CVD layer is comprised of at least two phases deposited simultaneously together, of which the first is composed of a member of the group of carbides, carbonitrides, nitrides, oxycarbides, oxycarbonitrides, suicides or borides of titanium, zirconium, hafnium, vanadium, niobium or tantalum, or a carbidesilicide or boride of chromium, molybdenum or tungsten, or a silicon or boron carbide and a second of these phases is selected from the group of oxides or oxynitrides of aluminum, titanium, zirconium, hafnium, magnesium, silicon and calcium or very stabilized zirconium oxide.
Of the deposited mentioned phases, at least one of the phases is composed of fibers, spikes or column-shaped particles with an elongated axial orientation extending in a direction which is perpendicular to the substrate/coating surface of the composite.